1. Field of the Invention
This invention relates to automatically operated dampers for burner flues.
2. Prior Art.
The typical flue from the burner of a hot water tank or furnace continually provides a free path for the flow of waste products of combustion. As a result, residual heat is lost from the heat exchanger by the stack effect of the flue, due to the continued flow of ambient air that enters the burner area and leaves through the stack after combustion has stopped. In addition, heat from the water in a hot water tank is lost to cooler air flowing through the portion of the flue that extends up the center of the tank. Moreover, a hot water tank flue typically has a draft diverter that, while limiting the stack effect or upward flow through the central flue of the tank, allows air to be drawn from the room, and ambient heat is lost through the flue. As a result of heat loss from furnaces and hot water tanks, fuel requirements are increased and the efficiency of operation is decreased. Such inefficiencies and the loss of heated room air has become a serious problem with the shortages and high cost of fuels.
Draft retarders are known for use in flues of heating systems. For example, U.S. Pat. No. 3,934,796 shows a solenoid operated damper energized by a heating system for automatic operation in a flue of the system. U.S. Pat. No. 3,010,451 shows a smoke pipe damper controlled by an electrically operated hydraulic motor. Other examples of automatically operated dampers are shown by U.S. Pat. Nos. 3,396,777 and 2,508,885. These arrangements utilize actuators that have disadvantageous characteristics and lack safety features and other advantages of the present invention, and fail to prevent heat loss associated with draft diverters.